366 DIGESTION 



destroys the diphtheria toxin, which is also rendered innocuous by 

 trypsin. Erepsin, however, is not specific to the secreted intestinal 

 juice, for it occurs also, not only in the mucous membrane of the 

 intestine, which, indeed, contains a greater quantity of it than the 

 succus entericus, but in all animal tissues hitherto investigated. It 

 is said even to be sometimes present in pancreatic juice, since in- 

 activated pancreatic juice, which does not digest other proteins, will 

 sometimes digest casein. But the matter is far from being settled, 

 and the presence of erepsin in the pancreatic tissue is a complicating 

 circumstance. For under abnormal conditions, most glands pro- 

 vided with artificial fistulae have an increased liability to injuries 

 of various kinds, which might permit constituents not normally 

 present in the secretion to pass into it from the cells. The kidney in 

 mammals is even richer in erepsin than the intestinal mucous 

 membrane. Next to these come the pancreas, spleen, and liver, 

 then at a long interval the heart muscle, while skeletal muscle and 

 brain-tissue are poorest of all in the ferment. The intestinal mucosa 

 varies in its erepsin content at different levels and on different diets. 

 In cats on a meat or a mixed diet the duodenum is about five times 

 richer in the ferment than the stomach. The ileum is about half as 

 rich as the duodenum, and the jejunum occupies an intermediate 

 position between the duodenum and ileum (Vernon). The secretion 

 of Brunner's glands in the duodenum, which resemble in structure 

 the pyloric glands of the stomach, digests coagulated albumin, 

 although its proteolytic powers are feebler than those of the pan- 

 creatic juice. 



Enterokinase. The most characteristic constituent of succus 

 entericus is a ferment, enter okinase, which differs from all the fer- 

 ments we have hitherto described in acting not directly upon the 

 foodstuffs, but upon the trypsinogen of the pancreatic juice, chang- 

 ing it into the active enzyme trypsin. It may therefore be spoken of 

 as a ferment of ferments. It has been previously stated that freshly 

 secreted pancreatic juice is without action upon proteins. The 

 addition of succus entericus immediately confers upon it a high 

 degree of proteolytic power. In one experiment pancreatic juice, 

 obtained by a temporary fistula, required four to six hours to dissolve 

 fibrin, and did not attack coagulated albumin even in ten hours. 

 On addition of succus entericus, the same pancreatic juice dissolved 

 fibrin in three to seven minutes, and rapidly digested coagulated 

 albumin (Pawlow). In like manner a glycerin extract of a fresh 

 pancreas has hardly any effect on proteins; a similar extract of a 

 stale pancreas is active. The fresh pancreas contains trypsinogen, 

 which is soluble in glycerin, for the inert extract becomes active 

 when it is treated with dilute acetic acid, or even when it is diluted 

 with water and kept at the body-temperature. If the fresh pancreas 

 be first treated with dilute acetic acid, and then with glycerin, the 



